1. Field of the Invention
The present invention relates to an ink ejector for forming an image on a recording medium such as recording paper by ejecting ink from a number of channels in accordance with print instructions.
2. Description of Related Art
Of all non-impact printers, ink jet printers have simple principles and are easy of multiple gradation and colorization. Drop-on-demand ink jet printers eject only droplets of ink for printing. Ink jet printers of this type are coming rapidly into wide use because of high ejection efficiency and low running costs.
For example, U.S. Pat. Nos. 4,879,568, 4,887,100, 4,992,808, 5,003,679, and 5,028,936, corresponding to Japanese Patent Application Laid-Open No. 63-247051, disclose an ink ejector of the shear mode type for use in a drop-on-demand printer, respectively. Piezoelectric material is used in the disclosed apparatus. The ejector ejects a series of ink droplets through one of nozzles to form a thick and clear image on a recording medium in accordance with the print instruction for one dot.
The viscosity of ink varies with temperature. As the temperature of ink rises, the ink viscosity lowers naturally. This causes ink droplets to be ejected in different manners by the ejector at a predetermined normal temperature (approx. 25 centigrade) and at a higher temperature (approx. 30-45 centigrade). At a higher temperature, ink may be ejected at such a pressure as can cause no ink ejection at a normal temperature, or ink may be spattered or splashed in fine particles. Some of the ink particles may stick to a nozzle plate which defines the nozzle. The surface tension of the ink sticking to the nozzle plate may cause the succeeding ink droplets to be ejected in wrong directions.
The ink temperature may be raised by higher ambient temperature, the heat generated from a controller of the ejector, the heat generated from deformation of the piezoelectric material when ink is ejected, and the heat generated from the carriage motor for moving the ejector relative to a recording paper.
If ink droplets are spattered or ejected in wrong directions, as stated above, excess ink droplets are ejected or ink droplets are ejected onto wrong spots, resulting in poor printing quality.
It has therefore been demanded to provide an ink ejector which can form a clear or sharp image not only at a normal temperature but also at a higher temperature.